1. Field of the Invention
This invention relates to conductive polymer PTC compositions and devices comprising them.
2. Introduction to the Invention
Conductive polymer compositions, and devices comprising them, are known. Reference may be made for example to U.S. Pat. Nos. 2,978,665, 3,243,753, 3,351,882, 3,571,777, 3,793,716, 3,823,217, 3,861,029, 4,017,715, 4,177,376, 4,188,276, 4,237,441, 4,238,812, 4,242,573, 4,246,468, 4,255,698 4,388,607, 4,426,339, 4,538,889 and 4,560,498; U.K. Patent No. 1,534,715; the article entitled "Investigations of Current Interruption by Metal-filled Epoxy Resin" by Littlewood and Briggs in J. Phys D: Appl. Phys, Vol. II, pages 1457-1462; the article entitled "The PTC Resistor" by R. F. Blaha in Proceedings of the Electronic Components Conference, 1971; the report entitled "Solid State Bistable Power Switch Study" by H. Shulman and John Bartho (August 1968) under Contract NAS-12-647, published by the National Aeronautics and Space Adminstration; J. Applied Polymer Science 19, 813-815 (1975), Klason and Kubat; Polymer Engineering and Science 18, 649-653 (1978) Narkis et al; and commonly assigned U.S. Ser. Nos. 601,424 (Moyer), now abandoned, published as German OLS 2,634,999. For details of more recent developments in this field, reference may be made to copending and commonly assigned U.S. Ser. Nos. 67,207 (Doljack et al.) now abandoned in favor of continuation-in-part application Ser. No. 228,347, now Patent No. 4,450,496, 98,711 (Middleman et al.), now Patent No. 4,315,237, 141,984 (Gotcher et al.), 141,987 (Middleman et al.), now Patent No. 4,413,301 141,988 (Fouts et al.), 141,989 (Evans), 141,991 (Fouts et al.), 142,053 (Middleman et al.), now Patent No. 4,352,083, 142,054 (Middleman et al.), now Patent No. 4,317,027, 150,910 (Sopory), now Patent No. 4,334,351, 150,911 (Sopory), now Patent No. 4,318,881, 174,136 (Cardinal et al.), now Patent No. 4,314,230, 176,300 (Jensen), now Patent No. 4,330,704, 250,491 (Jacobs et al.), 254,352 (Taylor), now Patent No. 4,426,633, 272,854 (Stewart et al.), now abandoned in favor of continuation-in-part application Ser. No. 403,203, now Patent No. 4,502,929, 273,525 (Walty) now Patent No. 4,398,084 and 274,010 (Walty et al.), now abandoned. The disclosure of each of the patents, publications and applications referred to above is incorporated herein by reference.
Electrical devices containing conductive polymers generally (though not invariably) comprise an outer jacket, usually of insulating material, to protect the conductive polymer from damage by the surrounding environment. However, if no protective jacket is used, or if the jacket is permeable to harmful species in the environment, or if the conditions of use are such that the jacket may become damaged, it is necessary or desirable to select a conductive polymer which is not damaged (or which deteriorates at an acceptably low rate) when exposed to the surrounding environment. Exposure of conductive polymers to organic fluids generally results in an increase is resistivity; exposure to air, especially at elevated temperatures between room temperature and 35.degree. C. below the melting point generally results in a decrease in resistivity both at the elevated temperature and at room temperature (a phenomenon known in the art as "resistance relaxation").